1. Field of the Invention
The present disclosure relates to cutting tools and, more particularly, to surgical cutting instruments having elongate, inner and outer tubular members with distal ends cooperating to cut or resect bodily tissue.
2. Related Art
Elongate surgical cutting tools have been used in performing closed surgery, such as endoscopic surgery, i.e. arthroscopic surgery. FIG. 1 shows a surgical cutting instrument 10 for use in closed surgery. The cutting instrument 10 has an elongate outer tubular member 11 terminating at a distal end 12 having an opening 13 in the side wall and/or the end wall to form a cutting port or window and an elongate inner tubular member 20 (FIG. 2) coaxially disposed in the outer tubular member 11 and having a distal end 21 disposed adjacent the opening 13 in the distal end 12 of the outer tubular member 11. The distal end 21 of the inner tubular member 20 has a surface or edge 22 for engaging tissue via the opening 13 in the distal end 12 of the outer tubular member 11 and in many cases cooperates with the opening 13 to shear or cut tissue. A vacuum source (not shown) is coupled to the cutting instrument 10 and vacuums the tissue, and the irrigating fluid surrounding the tissue, out of the instrument 10. The outer and inner tubular members 11,20 each have a plastic hub 15,24 at their proximal ends 14,23. The hub 24 of the inner tubular member 20 has a transversely extending passage 25 therethrough, the inner tubular member 20 extending through an axial bore 26 in the hub 24 to communicate with the passage 25. A drive tang 27 within portion 28 is adapted to be driven via a hand piece (not shown) having a small electric motor therein controlled by finger-actuated switches on the hand piece. A foot switch or switches on a console supply power to the hand piece. FIGS. 1 and 2 represent components of a cutting instrument known in the industry as an end-bearing cutting instrument.
FIGS. 3 and 4 represent components of a cutting instrument known in the industry as a burr cutting instrument. The burr cutting instrument 30 also has an elongate outer tubular member 31 terminating at a distal end 32 having an opening 33 in the side wall and/or the end wall to form a cutting port or window and an elongate inner tubular member 40 (FIG. 4) coaxially disposed in the outer tubular member 31 and having a distal end 41 disposed adjacent the opening 33 in the distal end 32 of the outer tubular member 31. The distal end 41 of the inner tubular member 40 has a helical grooved surface or edge 42 for drilling and grinding tissue via the opening 33 in the distal end 32 of the outer tubular member 31 and in many cases cooperates with the opening 33 to shear or cut tissue. The inner tubular member 40 is likewise rotatably driven at its proximal end 43, normally via a hand piece having a small electric motor therein controlled by finger-actuated switches on the hand piece. A foot switch or switches on a console supply power to the hand piece.
Currently, the designs of both the end-bearing and burr cutting instruments utilize either a compression spring and a housing assembly (28,45) integrated into the inner tubular member (20,40) or a compression spring integrated into the driveshaft assembly of the hand piece unit (not shown). When a compression spring and a housing assembly 28 are integrated into the inner tubular member 20, the outer tip surface 29 of the inner tubular member 20 is preloaded against the inner tip surface 16 of the outer tubular member 11 in the case of end-bearing cutting instruments. Burr cutting instruments utilize a thrust washer 34 to preload the inner tubular member 40 against the outer tubular member 31, as there is no contact between the inner and the outer tip surfaces (46,35). The thrust washer 34 is a circular-shaped piece of polymer material. However, the washer 34 could be of another shape or type of material.
With either cutting instrument, the preload force is only generated once the cutting instrument is engaged in the hand piece unit. The preload force is the force involved in preloading components, such as the inner and outer tubular members, against one another. The amount of preload is dependent on the dimensional variation of the cutting instrument components and the hand piece unit. There are no means of retention of the inner tubular member within the outer tubular member unless the cutting instrument is engaged in the hand piece. In addition, the thrust washer arrangement makes the burr cutting instruments susceptible to excessive shedding and seizing. In use, the hand piece unit drives the inner tubular member against the outer tubular member, and especially in burr instruments, the washer breaks down and small pieces of shredded material from the washer become lodged in the drive tang/hand piece connection and, in some cases, inhibit the vacuum from suctioning the tissue and irrigating fluid. When this happens, the interface of the drive tang/hand piece, due to an insufficient amount of fluid in this area, may overheat causing seizing of the drive tang/hand piece and possible melting of the drive tang.
When a compression spring is integrated into the driveshaft assembly of a hand piece unit, there are no inner tubular member retention issues when the cutting instrument is disengaged from the hand piece unit. As shown in FIG. 5, a retainer 51 is integrated into the hub outer tubular member 50 to retain the inner tubular member 62 (FIG. 6) in the outer tubular member 52. In addition, as shown in FIG. 6, the inner tubular member 62 has a groove 63 at its proximal end 64 that the retainer 51 rests in to retain the inner tubular member 62 when the inner tubular member 62 is disposed into the outer tubular member 52. The tool that is shown in FIGS. 5 and 6 is an end-bearing cutting tool. However, a retainer can also be used with a burr cutting tool. The design of having the compression spring integrated into the driveshaft assembly is not feasible in small diameter cutting instrument applications due to size limitations of the compression spring and driveshaft.
A cutting instrument is needed whereby the preload force can be controlled more precisely. In addition, a cutting instrument having a design that avoids having to take into account the physical limitations of the driveshaft unit is needed. Furthermore, a cutting instrument that is simpler and less costly to make is also needed. Finally, a burr cutting instrument is needed that does not depend on the use of a thrust washer.